It is 19 years since the British Medical Association last thought it necessary to call a crisis meeting of its members in response to upheaval in the NHS. On that occasion, 26 March 1992, representatives of doctors across Britain debated John Major's attempt to reform the NHS by separating the purchasers of healthcare from the providers. On Tuesday a special representative meeting will take place again – this time to consider its position in relation to Andrew Lansley's plan to take the internal market of that era several stages further and prepare the NHS for privatisation.

Lansley has a problem; few of the BMA's 140,000 members believe his plans are sensible or will deliver what he claims. The British Medical Journal has dubbed the reforms "Dr Lansley's Monster", the National Audit Office has warned that the quality of service offered by GPs could drop, and the King's Fund has pointed out the government runs the risk of replacing the bureaucracy of performance management with the red tape of economic regulation.

This mother of all reforms plans to further extend the healthcare market within the health service in England, fronted by GPs, herded en masse into commissioning consortiums. They will be given £80bn of public funds to buy healthcare from a system of competing providers under an "any willing provider" policy that will see private hospitals able to provide NHS care.

For professionals delivering care, the commercialisation of the health service will lead to a situation where clinical decision-making is increasingly influenced by financial considerations leading to the erosion of the social contract between doctors and patients. This is an affront to the public service ethos that glues the NHS together. The traditional role of doctors as the true advocates of patients will soon become history, just as it has in the US.

But the BMA has its own problem: many of its members believe its policy of "critical engagement" with the government over the NHS reform white paper that became the current health and social care bill has failed, and that it has to be more direct. Despite having more than 30,000 GPs in its ranks – the supposed winners from the shakeup – the BMA has been criticising the bill in increasingly strident tones. But the meeting will hear impassioned pleas for "critical engagement" to be replaced with outright opposition to the entire bill.

The BMA must grasp the nettle and unmask Lansley's reform agenda for what it is – the final step in the privatisation of the service. No amendments are going to turn this sow's ear into a silk purse, and the special representatives' meeting needs to vote in favour of rejecting the bill in its entirety. This would send out the strongest possible message that the grassroots of the medical profession have understood and rejected Lansley's ideologically driven plans.

The meeting should also recognise that a continuous evolution of the NHS is needed, with greater provider responsiveness and accountability. However, a high quality and efficient NHS will never be achieved using the market forces of "creative destruction". It is time to reject the market ideology that has plagued the NHS for more than 30 years and wasted billions of pounds, and move forward with a publicly funded, publicly provided, publicly accountable healthcare system based on co-operation, collaboration and the social contract between doctors and patients.

Tomorrow's meeting will be passionate and argumentative. There is a huge issue at stake: how doctors should respond to, and hopefully extinguish, plans that have little logic, support or justification. The BMA has world-class leaders. But at times such as these, when the core of the NHS is at risk, they can no longer simply wait and watch.